Quantifying wind and pressure effects on trace gas fluxes across the soil–atmosphere interface
Large uncertainties persist in estimates of soil–atmosphere exchange of important trace gases. One significant source of uncertainty is the combined effect of wind and pressure on these fluxes. Wind and pressure effects are mediated by surface topography: few surfaces are uniform and over scales of...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/7423/2015/bg-12-7423-2015.pdf |
| Summary: | Large uncertainties persist in estimates of soil–atmosphere
exchange of important trace gases. One significant source of uncertainty is
the combined effect of wind and pressure on these fluxes. Wind and pressure
effects are mediated by surface topography: few surfaces are uniform and over
scales of tenths of a metre to tens of metres, air pressure and wind speed at
the ground surface may be very variable. In this paper we consider how such
spatial variability in air pressure and wind speed affects fluxes of trace
gases. We used a novel nested wind tunnel design comprising a toroidial wind
tunnel, in which wind speed and
pressure may be controlled, set within a larger, linear wind tunnel. The
effects of both wind speed and pressure differentials on fluxes of CO<sub>2</sub>
and CH<sub>4</sub> within three different ecosystems (forest, grassland, peat bog)
were quantified. We find that trace gas fluxes are positively correlated with
both wind speed and pressure differential near the surface boundary. We argue
that wind speed is the better proxy for trace gas fluxes because of its
stronger correlation and because wind speed is more easily measured and wind
speed measurement methodology more easily standardized. Trace gas fluxes,
whether into or out of the soil, increase with wind speed within the toroidal
tunnel (+55 % flux per m s<sup>−1</sup>), while faster, localized surface
winds that are external to the toroidal wind tunnel reduce trace gas fluxes
(−13 % flux per m s<sup>−1</sup>). These results are consistent for both
trace gases over all ecosystem soil types studied. Our findings support the
need for a revised conceptualization of soil–atmosphere gas exchange. We
propose a conceptual model of the soil profile that has a "mixed layer",
with fluxes controlled by wind speed, wind duration, porosity, water table,
and gas production and consumption. |
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| ISSN: | 1726-4170 1726-4189 |